Enhanced selenium biofortification in tea plant by Co-applying Erwinia sp. PSI-03 and selenite: Rhizosphere microbiota restructuring and enhanced root foraging

Microbial-assisted biofortification represents a sustainable strategy to improve the efficiency of selenium (Se) fertilization for producing Se-enriched tea. However, whether microbial inoculation can jointly enhance rhizosphere Se availability and plant Se acquisition remains unclear. This study investigated the effects of co‑applying selenite with the Se-reducing bacterium Erwinia sp. PSI-03 on Se accumulation in tea plants, focusing on rhizosphere microbiota restructuring and root phenotypic adaptation. Results showed that although either Se fertilization or PSI-03 inoculation alone improved plant growth, the best performance was observed under their co-application. Compared with Se fertilization alone, co-application significantly increased both total and organic Se concentrations in spring-harvested tender leaves. At final harvest, it further increased Se accumulation across all plant organs, with increases of 32.1% and 40.8% in leaf total and organic Se concentrations, respectively. This increase was linked with a 26.3% rise in soil available Se and accompanied by an increased relative abundance of Bacillota , which was positively correlated with both soil available Se and plant Se concentrations. Functional prediction (PICRUSt2) indicated higher predicted abundances of bacterial genes (e.g., cysI , cysJ , nirS , metK , GST , and selA ) involved in Se transformation and mobilization under co-application. Co-application did not enhance root-to-stem or root-to-leaf Se translocation in plants, but enhanced root Se acquisition, accompanied by increased total root length, surface area, volume, and upregulated expression of transporter genes associated with Se acquisition ( CsPHO1;2 and CsPHT4;1a ). Additionally, root anatomical responses were selective, with a significant increase in cortex cell number. Collectively, this work highlights a potential mechanism underlying microbial-assisted Se-enriched tea production, in which co-application reshapes the rhizosphere microbiota and enhances root morphological development. These findings are helpful for the development of green biofortification strategies.